Cytotoxic T Lymphocyte Granzyme-b mediates neuronal cell death during Plasmodium berghei ANKA induced experimental cerebral malaria.

Cerebral malaria is a complex, acute, neurological disease characterised by a sudden onset of cerebral symptoms. This disease is manifested as initial arousable stage that is followed by an unarousable coma and eventually death. Parasite burden and CD8+ T cell count in the brain determines the disease outcome. Cytotoxic CD8+ T cell-derived Granzyme-b is required for the development of experimental cerebral malaria (ECM), but the mechanism of pathogenesis is not known. Here, we show that CD8+ T cells infiltrate in to the brain during ECM releasing Granzyme-b that is cytotoxic to neuronal cells. Granzyme-b kills neuronal cells through direct cytotoxicity and also by activating neuronal caspase-3 and calpain1 via cytoskeletal breakdown. Our results showed the increased expression of cell adhesion molecules and chemokine receptors in the brain and their associated infiltration of T cells during ECM.

Phenylhydrazine administration accelerates the development of experimental cerebral malaria.

Phenylhydrazine (PHZ) treatment is generally used to enhance parasitemia in infected mice models. Transient reticulocytosis is commonly observed in iron-deficient anemic hosts after treatment with iron supplementation, and is also associated with short-term hemolysis caused by PHZ treatment. In this study, we investigated the relationship between reticulocytosis and cerebral malaria (CM) in a murine model induced by PHZ administration before Plasmodium berghei ANKA (PbA) infection. Mortality and parasitemia were checked daily. Pro-inflammatory cytokines and IL-10 were quantified by ELISA. The expression of CXCL9, CXCL10, CCL5, and CXCR3 mRNAs was determined by real-time PCR. Brain sequestration of CD4(+) and CD8(+) T cells and populations of splenic Th1 CD4(+) T cells, dendritic cells (DCs), CD11b(+) Gr1(+) cells, and regulatory T cells (Tregs) were assessed by FACS. PHZ administration dramatically increased parasitemia from day 3 to day 5 post infection (p.i.) compared with the untreated control infected mice group; also, CM developed at day 5 p.i., compared with day 7 p.i. in untreated control infected mice, as well as significantly decreased blood-brain barrier function (P < 0.001). PHZ administration during PbA infection significantly increased the expression of CXCL9 (P <0.05) and VCAM-1 (P <0.001) in the brain, increased the expression of CXCL10, CCL5 and CXCR3, and significantly increased the recruitment of CD4(+) and CD8(+) T cells (P <0.001 and P <0.01, respectively) as well as CD11b(+) Gr1(+) cells to the brain. In addition, PHZ administration significantly increased the numbers of IL-12-secreting DCs at days 3 and 5 p.i. compared to those of untreated control infected mice (P <0.001 and P <0.01, respectively). Consequently, the activation of CD4(+) T cells, especially the expansion of the Th1 subset (P <0.05), was significantly and dramatically enhanced and was accompanied by marked increases in the production of protein and/or mRNA of the Th1-type pro-inflammatory mediators, IFN-γ and TNF-α (P <0.01 for both for protein; P <0.05 for TNF-α mRNA). Our results suggest that, compared to healthy individuals, people suffering from reticulocytosis may be more susceptible to severe malaria infection in malaria endemic areas. This has implications for the most appropriate selection of treatment, which may also cause reticulocytosis in patients living in such areas.

Reduction of experimental cerebral malaria and its related proinflammatory responses by the novel liposome-based ß-methasone nanodrug.

Cerebral malaria (CM) is a severe complication of and a leading cause of death due to Plasmodium falciparum infection. CM is likely the result of interrelated events, including mechanical obstruction due to parasite sequestration in the microvasculature, and upregulation of Th1 immune responses. In parallel, blood-brain-barrier (BBB) breakdown and damage or death of microglia, astrocytes, and neurons occurs. We found that a novel formulation of a liposome-encapsulated glucocorticosteroid, ß-methasone hemisuccinate (nSSL-BMS), prevents experimental cerebral malaria (ECM) in a murine model and creates a survival time-window, enabling administration of an antiplasmodial drug before severe anemia develops. nSSL-BMS treatment leads to lower levels of cerebral inflammation, expressed by altered levels of corresponding cytokines and chemokines. The results indicate the role of integrated immune responses in ECM induction and show that the new steroidal nanodrug nSSL-BMS reverses the balance between the Th1 and Th2 responses in malaria-infected mice so that the proinflammatory processes leading to ECM are prevented. Overall, because of the immunopathological nature of CM, combined immunomodulator/antiplasmodial treatment should be considered for prevention/treatment of human CM and long-term cognitive damage.

Therapeutical targeting of nucleic acid-sensing Toll-like receptors prevents experimental cerebral malaria.

Excessive release of proinflammatory cytokines by innate immune cells is an important component of the pathogenic basis of malaria. Proinflammatory cytokines are a direct output of Toll-like receptor (TLR) activation during microbial infection. Thus, interference with TLR function is likely to render a better clinical outcome by preventing their aberrant activation and the excessive release of inflammatory mediators. Herein, we describe the protective effect and mechanism of action of E6446, a synthetic antagonist of nucleic acid-sensing TLRs, on experimental cerebral malaria (ECM) induced by Plasmodium berghei ANKA. We show that in vitro, low doses of E6446 specifically inhibited the activation of human and mouse TLR9. Tenfold higher concentrations of this compound also inhibited the human TLR8 response to single-stranded RNA. In vivo, therapy with E6446 diminished the activation of TLR9 and prevented the exacerbated cytokine response observed during acute Plasmodium infection. Furthermore, severe signs of ECM, such as limb paralysis, brain vascular leak, and death, were all prevented by oral treatment with E6446. Hence, we provide evidence that supports the involvement of nucleic acid-sensing TLRs in malaria pathogenesis and that interference with the activation of these receptors is a promising strategy to prevent deleterious inflammatory responses that mediate pathogenesis and severity of malaria.

Overwhelming parasitemia with Plasmodium falciparum infection in a patient receiving infliximab therapy for rheumatoid arthritis.

We describe a 45-year-old woman receiving infliximab therapy for rheumatoid arthritis who developed an overwhelming Plasmodium falciparum infection with cerebral malaria. Physicians should be aware that patients receiving tumor necrosis factor inhibitors, such as infliximab, may be at increased risk of life-threatening malarial infections.

Malaria mimicry with tumor necrosis factor. Contrasts between species of murine malaria and Plasmodium falciparum.

Because Plasmodium berghei ANKA induces cerebral malaria and P. vinckei does not, the former has often been studied as a model for human falciparum malaria. It lacks, however, many of the systemic changes seen in the human disease. Because both of these murine models and the human disease have now been defined in terms of excess tumor necrosis factor (TNF) production, the authors have more closely examined the two murine models in this light to see which provides the better overall model for falciparum malaria. Administering TNF to malaria-infected mice did not cause cerebral symptoms nor breakdown of the blood-brain barrier, which is the hallmark of P. berghei ANKA cerebral malaria and is generally absent in human cerebral malaria. Tumor necrosis factor did, however, induce hypoglycemia and liver injury, pathology that is seen in terminal P. vinckei and falciparum malaria, but is absent in terminal P. berghei ANKA malaria. Plasma TNF and interleukin-6 (IL-6) also were found to be consistently higher in infections caused by P. vinckei than in those caused by P. berghei ANKA. The pathology of P. vinckei malaria is thus consistent with raised systemic levels of TNF and other cytokines, as is falciparum malaria. The authors therefore conclude that P. vinckei malaria, although lacking a cerebral component, is the better model for the human disease.